1. Field of the Invention
This invention relates to gasification of carbonaceous materials, and more particularly to apparatus for removal of ash from fluidized bed gasification reactors.
2. Description of the Prior Art
In reactors for the gasification of carbonaceous materials, such as coal, a combustible product gas is produced, as well as solid waste products such as agglomerated ash. In the Process Development Unit (PDU) fluidized bed gasification reactor being operated for the U.S. Government, particulate coal is injected through the central one of a number of concentric tubes extending upwardly into the center of a vertical bed-containing pressure vessel. Fluidization occurs in the upper sections.
Fluidization and combustion support gases have been injected into the PDU in various manners, including vertically through the concentric tubes, radially from the concentric tubes, and through sparger rings disposed at selected elevations within the vessel. Other gasification reactors discharge a fluidizing gas into vertical vessels through perforated plates positioned near the bottom of the vessel.
In the PDU fluidized bed gasification reactor, particulated feed coal, in addition to producing a combustible product gas, intermediately forms char, and ultimately forms waste ash. The process takes place at temperatures in the range of 1400.degree. F. to 1900.degree. F., and above. The ash must be removed from the vessel, preferably continuously or by an on-line batch process, in order to maintain the process efficiently operational. It is also desirable to remove the ash at a low temperature, less than about 500.degree. F., to minimize the impact of heat transfer on downstream components and to decrease heat loss. This can necessitate a long vessel with an elongated lower section through which downward movement of the dense ash takes place over an extended period of time, thus allowing sufficient cooling of the ash prior to removal from the vessel.
As the ash cools, it tends to agglomerate in large particles. If left untreated, in a continuous flow process, the cooling of the ash would be impeded and it is possible the elongated lower section of the vessel could become fouled or plugged. These particles are sometimes large enough to block ash removal through a starwheel feeder located at the bottom of the gasifier. Additionally, after removal from the gasification system, particles of a maximum size or smaller are easier to handle.
It is thus desirable to provide gasifiers with an effective means fo reducing particulate waste to a maximum size, allowing such waste to cool from gasifier temperature and removing such waste from the gasifier system.